U.S. patent number 3,638,157 [Application Number 04/828,466] was granted by the patent office on 1972-01-25 for combination motor starter.
This patent grant is currently assigned to Westinghouse Electric Corporation. Invention is credited to Zelco J. Kruzic.
United States Patent |
3,638,157 |
Kruzic |
January 25, 1972 |
COMBINATION MOTOR STARTER
Abstract
An improved combination motor starter with low overload
protection; adjustable low-level fault protection; heavy short
circuit interrupting capacity; and a coordinated protection system
that protects the motor, the cable and the components of the
combination motor starter. More specifically, the low-level fault
protection is given by a resettable circuit breaker, and a
current-limiting fuse is used both to provide heavy short circuit
protection and to also operate fast enough and at low enough
currents to protect against burnout or damage of the heater or
other current-responsive element of the device protecting the motor
against overloads.
Inventors: |
Kruzic; Zelco J. (New Brighton,
PA) |
Assignee: |
Westinghouse Electric
Corporation (Pittsburgh, PA)
|
Family
ID: |
25251885 |
Appl.
No.: |
04/828,466 |
Filed: |
May 28, 1969 |
Current U.S.
Class: |
337/6 |
Current CPC
Class: |
H01H
89/06 (20130101); H02H 7/08 (20130101); H01H
71/1081 (20130101); H01H 71/12 (20130101) |
Current International
Class: |
H01H
71/12 (20060101); H01H 89/06 (20060101); H01H
71/10 (20060101); H02H 7/08 (20060101); H01h
085/00 () |
Field of
Search: |
;337/6,49,48,78,38,107,161,7,54 ;317/13,37,116 ;335/9,126,142
;318/221 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Broome; Harold
Claims
I claim:
1. A combination motor starter for controlling a motor circuit
having a predetermined full-load motor current, said motor starter
comprising current-responsive low overload protecting means
operable with a time delay upon the occurrence of overloads of a
first predetermined current and higher to effect interruption of
said motor circuit, said current-responsive low overload protecting
means comprising a contactor and overload relay means operable with
a time delay upon the occurrence of said overloads of said first
predetermined current and higher to automatically effect operation
of said contactor to interrupt said motor circuit, said motor
starter comprising current-responsive fault-protecting means
operable within a fraction of a second upon the occurrence of
overloads of and above a second predetermined current and higher to
interrupt said motor circuit, said current-responsive fault-current
protecting means comprising an automatic tripping resettable
circuit breaker and current-limiting means, and said
current-limiting means effectively operating to limit the current
that said current-responsive fault-current protecting means
interrupts at fault currents starting at a predetermined fault
current within the range of from 50 to 200 times said full-load
motor current.
2. A combination motor starter according to claim 1, and said
current-limiting means effectively operating to limit the current
that said current-responsive fault-current protecting means
interrupts at fault currents starting at a predetermined fault
current within the range of from 100 to 150 times said full-load
motor current.
3. A combination motor starter according to claim 1, said first
predetermined current being a current within the range of between
one and two times said full-load motor current, and said second
predetermined current being a current within the range of between
three and 13 times said full-load motor current.
4. A combination motor starter for controlling a motor circuit
having a predetermined full load current, said motor starter
comprising current-responsive low-overload protecting means
operable with a time delay upon the occurrence of overloads of a
first predetermined current and higher to effect interruption of
said motor circuit, said low-overload protecting means comprising a
contactor and an overload relay operable with a time delay upon the
occurrence of said overloads of said first predetermined current
and higher to effect operation of said contactor to thereby effect
interruption of said motor circuit, an automatic-tripping
resettable circuit breaker automatically operable faster than said
low-overload protecting means upon the occurrence of overloads on
and above a second predetermined current higher than said first
predetermined current to interrupt said motor circuit,
current-limiting fuse means automatically operable faster than said
circuit breaker upon the occurrence of overloads on and above a
third predetermined current higher than said second predetermined
current to interrupt said motor circuit, said first predetermined
current being a current within the range of from one to two times
said full-load current, said second predetermined current being
within the range of from two to 13 times said full load current,
and said third predetermined current being within the range of from
50 to 200 times said full load current.
5. A combination motor starter according to claim 4, said circuit
breaker comprising a unitary molded-case type circuit breaker, and
said current-limiting fuse means comprising a unitary molded-case
type fuse unit removably connected to said unitary molded case-type
circuit breaker.
6. A combination motor starter according to claim 5, said
combination motor starter comprising an enclosure, said contactor
said overload relay said circuit breaker and said current-limiting
fuse means being supported within said enclosure, said circuit
breaker comprising an operating handle, and an external handle
mechanism on said enclosure operatively connected to said operating
handle to permit external manual operation of said circuit
breaker.
7. A combination motor starter according to claim 4, said first
predetermined current being a current within the range of from one
to 1.5 times said full-load current, said second predetermined
current being a current within the range of from four to 13 times
said full-load current, and said third predetermined current being
within the range of from 100 to 150 times said full-load
current.
8. A combination motor starter according to claim 7, said second
predetermined current being a current within the range of from five
to 13 times said full-load current, and said circuit breaker
comprising magnetic-only trip means operable within one-half of a
second and no longer to operate within the full range from said
second predetermined current to said third predetermined current to
trip said circuit breaker to interrupt said motor circuit.
9. A combination motor starter according to claim 8, said circuit
breaker comprising a unitary insulating housing-type circuit
breaker, said current-limiting fuse means comprising a unitary
insulating housing-type fuse unit, said combination motor starter
comprising an enclosure, said fuse unit said circuit breaker said
contactor and said overload relay means being mounted in said
enclosure, and said combination motor starter comprising externally
operable operating means operatively connected to said circuit
breaker.
10. A combination motor starter for controlling a motor, said
combination motor starter including a motor overload responsive
device, an excess current responsive resettable circuit breaker
separate from said motor overload responsive device, and a
current-limiting fuse means, said motor overload responsive device
having a time-current characteristic which is faster than both said
excess current-responsive circuit breaker and said current-limiting
fuse means to interrupt the current to said motor upon the flow of
overload current occasioned by an overload on the motor, said
excess current-responsive circuit breaker operating faster than
said current-limiting fuse means to interrupt the current to said
motor on low-level fault currents above motor overload currents,
and said current-limiting fuse means being faster than the excess
current-responsive circuit breaker to interrupt the current to said
motor on heavier fault currents which could cause damage to the
motor overload responsive device before the circuit breaker
operates on such heavier fault currents.
11. A combination motor starter according to claim 10, said motor
overload responsive device comprising thermal actuating means
automatically operable with a time delay to effect interruption of
overload currents within a first full range from a first current to
a second current, said circuit breaker comprising magnetic tripping
means operating always within one-half of a second to trip said
circuit breaker to interrupt low-level fault currents within a
second full range from said second current to a third current, and
said current-limiting fuse means operating to interrupt heavier
fault currents within a third full range from said third current to
the maximum current that said combination motor starter can
interrupt.
12. A combination motor starter according to claim 11, said thermal
actuating means having a time-current damage curve, said circuit
breaker protecting said thermal actuating means from damage within
said second full range, and said current-limiting fuse means
protecting said thermal actuating means from damage within said
third full range.
13. A combination motor starter according to claim 12, said circuit
breaker comprising a unitary insulating housing-type circuit
breaker, and said fuse means comprising a unitary insulating housin
type fuse device removably connected to said circuit breaker.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS AND PATENTS
Components of the subject combination motor starter are of the
general type, more specifically described in the U.S. Pat. Nos.
3,265,831, 3,296,567 and 3,296,393, and in the applications Ser.
No. 703,409, filed Feb. 6, 1968 now U.S. Pat. No. 3,575,679, and
Ser. No. 752,848, filed Aug. 15, 1968. The patents and applications
will be further identified in the specification hereinafter with
reference to the components of the combination motor starter.
BACKGROUND OF THE INVENTION
1. Field of the Invention
Combination motor starter for controlling and protecting motors and
motor circuits.
2. Description of the Prior Art
It is old in the art to provide a fuse-switch combination motor
starter comprising a contactor with overload relays for
automatically opening the contactor to open the motor circuit upon
the occurrence of lesser overload currents occasioned by overloads
on the motor; current-limiting fuses for interrupting low-level to
high-level and short-circuit fault currents; and a manually
operable switch for permitting manual opening and closing of the
motor circuit.
It is also old in the art to provide a fuse-breaker combination
motor starter comprising a contactor with overload relays for
opening the contactor to open the motor circuit upon the occurrence
of lesser overload currents; a manually operable circuit breaker
automatically operable to interrupt the motor circuit upon the
occurrence of low-level to high-level faults and current-limiting
fuses that operate upon the occurrence of a heavy short-circuit
current having a value in a range from just below the interrupting
rating of the breaker to a value above the interrupting rating of
the breaker to interrupt the circuit with a current-limiting action
and to trip the circuit breaker, the circuit breaker and fuse
time-current curves being coordinated as described in Dyer U.S.
Pat. No. 3,077,525, issued Feb. 12, 1963.
SUMMARY OF THE INVENTION
The invention provides an improved combination motor starter
providing an improved coordinated protection system. The device
includes a circuit-interrupting device for opening the circuit to
the motor and a motor overload responsive device for initiating
opening of the motor circuit with a time delay upon the flow of an
overload current in the range between a current above the full-load
current to the motor and the locked rotor current of the motor.
There is a current-responsive device operable upon the flow of an
excess current greater than the locked rotor current of the motor
and this current-responsive device initiates the opening of the
motor circuit faster than the motor overload responsive device.
There is also a current-limiting device operative upon the flow of
heavier excess currents to limit the current flow to a value which
does not damage the motor overload responsive device. More
specifically, the starter comprises a contactor, overload means for
operating the contactor and an adjustable current-limiting circuit
interrupter for interrupting fault currents to protect the motor,
cable and the components of the starter. The overload relay means
operates, with a time delay, upon the occurrence of motor overloads
of, for example, 1.25 times full-load current of the motor and
higher up to locked rotor current, to effect opening of the
contactor. The adjustable current-limiting circuit interrupter
operates, faster than the relay means, to interrupt the motor
circuit upon the occurrence of fault currents starting at a
predetermined current within the range of from two to 13 times
full-load current. Preferably the circuit interrupter comprises a
manually operable adjustable automatic tripping resettable circuit
breaker that automatically trips, faster than the relay means, from
a first predetermined overload current within the range of from two
to 13 times full-load current, and preferably within the range of
from five to 13 times full-load current; and a current-limiting
fuse device that operates, faster than the circuit breaker, to
interrupt fault currents from a second predetermined overload
within a second range of from 50 to 200 times full-load current,
and preferably within the range of from 100 to 150 times full-load
current.
During interruption by the current-limiting fuse unit the circuit
breaker sees enough current to automatically trip the breaker. This
opens all conductors leading to the motor and prevents single-phase
operation of three-phase motors, whereas if only fuses were
provided, one might blow and allow the motor to operate on single
phase. The current-limiting fuse unit provides an effective
interrupting capacity of 100,000 amperes at 600 volts even though
the interrupting capacity of the circuit breaker may be only 10,000
amperes. The circuit breaker is a motor circuit protector. Each
motor has a different locked rotor current value. Thus, each motor
should be protected by a circuit breaker with precisely the right
tripping point.
The circuit breaker utilized in this combination is preferably
externally adjustable and comprises selective locking means for
providing that the trip adjustment cannot be set higher than the
maximum locked rotor current, which may be about 13 times the
full-load current of the motors that are to be protected by the
breaker.
The fuse unit is removably mounted and connected to the circuit
breaker, providing the advantage that the circuit interrupter or
fused circuit breaker combination can be made up utilizing a
circuit breaker that has utility without the fuse unit.
The novel combination of this invention has an advantage over the
above-mentioned fused switch combination motor starter in that the
circuit breaker is adjustable and resettable following tripping
operations of the breaker. Another advantage of the novel
combination of this invention is that in the low-level fault area
the magnetic trip device of the circuit breaker will clear a fault
faster than a fuse which is inherently a thermal sensing device
with a built-in time delay to override the initial inrush peaks. In
the subject invention the breaker comprises a magnetic trip that is
a constant-time device requiring one-half to three-fourths of a
cycle to clear in the area of low-level faults. In the area of
low-level faults, which comprise the majority of faults
encountered, the breaker will clear the circuit perhaps 10 to 15
cycles faster than a fuse.
The novel combination of this invention has an advantage over the
above-mentioned fused-breaker combination motor starter in that the
time-current tripping curve characteristics of the combination of
this invention are such that the current-limiting fuses serve to
interrupt the circuit and limit the current at a current level that
otherwise could cause heater burnout and damage of the overload
relays and also possible damage to the contactor itself.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a top plan view, with parts broken away, of a combination
motor starter constructed in accordance with principles of this
invention;
FIG. 2 is a schematic wiring diagram illustrating an application of
the motor starter of FIG. 1;
FIG. 3 is a side sectional view through the center pole unit of the
circuit interrupter of FIG. 1;
FIG. 4 is a partial view illustrating the trip-adjusting means and
locking means for selectively changing the range of adjustment of
the circuit breaker of FIG. 3;
FIG. 5 is a side sectional view through one of the pole units of
the multipole contactor of FIG. 1;
FIG. 6 is a plan sectional view of the multipole overload relay of
FIG. 1;
FIG. 7 is a side sectional view taken generally along the line
VII--VII of FIG. 6; and
FIG. 8 is a diagram of the combination time-current characteristics
of an application of the combination motor starter of this
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to the drawings, there is disclosed in FIG. 1, a
combination motor starter 5 comprising an enclosure 7, a circuit
interrupter 8 that comprises a multipole circuit breaker 9 and a
multipole fuse unit 11, a multipole contactor 13, and a multipole
overload relay 15.
The enclosure 7 is of the type more specifically described in the
patent to R. V. Rimmer et al. U.S. Pat. No. 3,296,393, issued Jan.
3, 1967. Thus, only a brief description of the enclosure will be
provided herein. The enclosure 7 comprises a receptacle 17 having a
front flange portion 19 thereon and a hinged cover (broken away) 21
movable to open and close the receptacle. A handle operating
mechanism 23 extends from the flange portion 19 to permit external
manual operation of the circuit breaker 9. A claw-type member 25,
which is operated by the handle operating mechanism 23, is
operatively connected to the handle 27 of the circuit breaker 9 to
manually operate the circuit breaker 9 upon operation of the handle
operating mechanism 23.
The circuit breaker 9 is of the type more specifically described in
the application of James P. Ellsworth et al., Ser. No. 703,409,
filed Feb. 6, 1968. Thus, only a brief description of the circuit
breaker will be provided herein. The circuit breaker 9 (FIG. 3)
comprises an insulating housing 29 having an opening in the front
thereof through which the handle 27 extends. The circuit breaker is
a three-pole circuit breaker with the center pole unit being shown
in FIG. 3. Each pole unit comprises a conducting strap 31 having a
terminal connector 33 at the outer end thereof and a stationary
contact 35 at the inner end thereof; a movable contact arm 37
having a movable contact 39 thereon; a switch arm 41 pivotally
carrying the contact arm 37 at one end thereof and being fixedly
connected to a common insulating tie bar 43 at the other end
thereof; a flexible conductor 45 connected at one end thereof to
the associated contact arm 37 and at the other end thereof to a
terminal 47; and a coil 49 connected at one end thereof to the
terminal 47 and at the other end thereof to a terminal 51. The
circuit for each pole unit extends from the terminal connector 33
through the conductor 31, stationary contact 35, movable contact
39, contact arm 37, flexible conductor 45, terminal conductor 47,
coil 49, to the terminal 51.
In the center pole unit a toggle 53, comprising a pair of pivotally
connected toggle links, is pivotally connected at one end to the
center pole switch arm 41 and at the other end to a releasable trip
member 55 that is mounted for pivotal movement on a pin 57. A pair
of overcenter tension springs 59 are connected at one end thereof
to the knee pivot of the toggle 53 and at the other end thereof to
the bight portion of an inverted U-shape operating lever 61. The
operating lever 61 is pivotally supported at the inner ends of the
legs thereof on a pair of stationary supporting plates in a
well-known manner. The handle 27 is connected to the lever 61 to
provide for manual operation.
The releasable trip member 55 is latched at the free end thereof,
against clockwise (FIG. 3) tripping movement, by means of a roller
latch member 63 that is pivotally mounted on a pin 65. The trip
member 55 is latched by a roller 64 that is supported for movement
in a slot on the member 63 and biased to the latching position by
means of a torsion spring 66. The roller latch member 63 is latched
against clockwise unlatching movement by means of an insulating
trip bar 67 that is common to all three pole units and that is
supported for pivotal movement about the elongated axis thereof,
which axis is normal to the plane of the paper as seen in FIG.
3.
In each pole unit, an electromagnetic trip device comprises the
coil 49, a stationary magnetic member 69, that is supported within
the coil 49, and a movable magnetic armature 71 that is supported
for pivotal movement about a pin 73. Each armature 71 comprises an
extension 75 having an actuating screw 77 threadedly secured
thereto at the upper end thereof. Each of the actuating screws 77
extends through an opening in a common adjusting bar 79 that is
pivotally supported at the opposite ends thereof on the ends of the
tie bar 67.
A single adjusting cam member 81 (FIG. 4), comprising a cam surface
83 that cooperates with the adjusting bar 79, is supported within
the breaker for movement about an axis normal to the plane of the
paper as seen in FIG. 4. A lockpin 85 is selectively mountable in a
selected one of a plurality of openings (FIG. 1) in the front of
the housing to change the range of adjustment of the tripping
characteristics of the circuit breaker in the manner more
specifically described in the above-mentioned application of James
P. Ellsworth et al., Ser. No. 703,409, now U.S. Pat. No.
3,575,679.
Referring to FIG. 3, the circuit breaker 9 is shown in the closed
position. The circuit breaker is manually operable to the open or
"off" position by counterclockwise movement of the handle 27, which
movement changes the line of action of the springs 59 to cause
collapse of the toggle 53 and simultaneous opening movement of the
contact arms 37. The circuit breaker is manually closed by
clockwise movement of the handle 27 to the "on" or closed position
which movement changes the line of action of the springs 59 to
cause erection of the toggle 53 and simultaneous closing movement
of the three contact arms in a manner well known in the art.
With the circuit breaker in the closed position, when an overload
within the tripping range of the circuit breaker 9 occurs in any of
the pole units the armature 71 of that pole unit will be attracted
to the magnet 69 whereupon the associated screw 77 will engage the
trip bar 67 to pivot the trip bar 67 in a counterclockwise
direction to release the roller latch member 63 which then releases
the trip member 55. Upon release of the trip member 55 the springs
59 rotate the trip member 55 in a clockwise direction to the
tripped position changing the line of action of the springs 59
which operate to collapse the toggle 53 to effect opening movement
of the three contact arms 37.
Following the automatic tripping operation, the circuit breaker 9
must be reset and relatched before the breaker can again be closed.
Resetting and relatching is effected by moving the handle 27 to a
position slightly past the full "off" position. During this
movement, a projection 89 on the operating lever 61 engages a
shoulder 91 on the trip member 55 to pivot the trip member 55 in a
counterclockwise direction. During this movement the trip member 55
wipes by the roller 64 and engages a part of the roller latch
member 63 to move the roller latch member 63 to the latching
position, whereupon spring means 95 biases the trip bar 67 into the
latching position wherein the trip bar 67 again latches the roller
latch member 63 so that upon release of the handle 27 the roller
latch member 63 will again latch the releasable trip member 55
against clockwise tripping movement. Thereafter, the circuit
breaker 9 can be manually and automatically operated in the same
manner as was hereinbefore described.
The fuse unit 11 is a multipole fuse unit constructed generally in
the manner described in the above-mentioned patent application of
James C. Wilson Ser. No. 752,848, filed Aug. 15, 1968, except that
the fuses of the fuse unit 11 are constructed to interrupt the
circuit at a significantly lower level of fault current than the
fuses of the application Ser. No. 752,848, which were specifically
designed to operate within and close to the interrupting capacity
of the circuit breaker of the fused-breaker combination. That is,
the current-limiting fuses of this invention will blow faster than
the circuit breaker will trip on currents just below those currents
which could cause heater burnout or overload relay damage, whereas
the fuses formerly used did not blow until close to the
interrupting capacity of the circuit breaker which is often 10,000
amperes or more and way beyond the currents which cause heater
burnout or relay damage.
The fuse unit 11 comprises an insulating fuse unit housing 99
having insulating barrier means forming three adjacent compartments
therein for the three poles of the fuse unit. Each pole unit
comprises a pair of terminal conductors 101, 103 supported therein
and having the bent-over lower leg portions extending out from
opposite ends of the housing 99. The terminal 101 of each pole unit
is connected to the associated pole unit of the circuit breaker 9
by means of a bolt member 105. A separate solderless terminal
connector 107 is mounted on the end portion of each of the
terminals 103. A plurality of fusible elements 109 (6 as seen in
FIG. 3) are connected between the spaced faces of the conductors
101, 103. A fusible strain wire 112 is connected to an indicator
113 that is biased by a spring 114.
The inside cavity of each pole unit is filled with an arc-quenching
filler material 117, such as sand. Upon the occurrence of an
overload in any of the pole units, in the operating range of the
fuse unit, the fusible elements 109, which are in parallel in the
circuit of the associated overloaded pole unit, will fuse or blow
instantaneously to interrupt the overload with a current-limiting
action. The heat that is generated by the circuit interruption is
conducted through the filler material to the fusible strain wire
112 which fuses, whereupon the spring 114 biases the indicator 113
frontward to provide a visual indication that the fuse has
blown.
When a maintenance man sees that a particular fuse has blown, he
can remove the fuse device and replace the blown fuse in the
housing 99 with a similar fuse. During the course of replacing the
blown fuse, the filler material 117 can be replaced with filler
material that has not been subjected to a circuit interruption.
Thereafter, the fuse device 11 can be installed and connected to
the circuit breaker 9.
The contactor 13 (FIGS. 1 and 5) is of the type disclosed in the
patent to John P. Conner et al. U.S. Pat. No. 3,296,567, issued
Jan. 3, 1967. Thus, only a brief description of the contactor 13
will be provided herein. The contactor 13 comprises a metallic
baseplate 123 with an insulating housing structure 125 supported
thereon. A U-shaped magnetic core member 127 is stationarily
mounted on the baseplate 123 within the housing 125. A coil 129,
comprising conducting coil means supported in an insulating
capsule, is supported in the housing 125. A U-shaped magnetic
armature 131 is supported for vertical (FIG. 5) rectilinear
movement toward and away from the pole faces of the stationary
magnetic member 127. An insulating contact carrier 133, spring
biased to the unactuated position by spring means 135, is connected
to the armature 131 to move with the armature 131.
The contactor 13 is a four-pole contactor with each pole unit
comprising a pair of stationary contacts 137, 139 and a movable
bridging contact member 141. Each of the bridging contact members
141 is supported on the insulating contact carrier 133 for movement
with the contact carrier 133 between open and closed positions. A
separate contact-pressure spring means 143 is provided at each pole
unit to provide contact pressure between the bridging contact
member 141 and the associated stationary contacts 137, 139. In each
pole unit, the stationary contact 139 is supported on a conducting
strap 147 and the stationary contact 137 is supported on a
conducting strap 149. Suitable terminal means 150, 152 (FIG. 1) are
connected to the outer ends of the straps 147, 149 to permit
connection of each pole unit in an electric circuit. Externally
accessible terminals 153, 154 (FIG. 1) are provided for enabling
connection of the coil 129 in an electric circuit.
The contactor is shown in FIG. 5 in the deenergized or unactuated
position with the bridging contact member 141 in the normally open
position and the armature 131 in the upper unactuated position.
Upon energization of the coil 129, the armature 131 is attracted
downward toward the stationary magnetic member 127 to
simultaneously move the four bridging contact members 141 of the
four-pole units from the open position seen in FIG. 5 to the closed
position. Upon deenergization of the coil 129, the springs 135
return the armature 131 and contact carrier 133 to the unactuated
normally open position seen in FIG. 5.
The multipole overload relay 15 is of the type more specifically
described in the patent to J. B. Ramsey et al. U.S. Pat. No.
3,265,831, issued Aug. 9, 1966. Thus, only a brief description of
the relay 15 will be provided herein. The relay 15 comprises an
insulating housing 153. A separate actuating bimetal 155, for each
of the pole units, is suitably supported in the housing 153. For
each pole unit, a separate replaceable heater member 157 is
removably secured in place by means of screws 159, 161, and a
separate pair of terminals 163, 165 are provided to enable
connection of each of the heater members 157 in an electric
circuit.
An insulating actuating bar 169, common to all three-pole units, is
pivotally supported at 171 (FIG. 7). The actuating bar 169
comprises a projection 173 (FIG. 6) that engages a compensating
bimetal 175 that is connected to an operating structure 177. Upon
movement of the compensating bimetal 175, the operating structure
177 is operated to move a movable contact arm 179 that carries a
movable contact 181 thereon for cooperating with a stationary
contact 183 that is mounted on a stationary contact arm 185.
The relay is seen in FIG. 6 in the normally closed position. When
the relay is in the normally closed position, a circuit extends
from a terminal 187 through a conducting bracket 189, the movable
contact arm 179, the movable contact 181, the stationary contact
183, the stationary contact arm 185, to a terminal 191. As is more
specifically described in U.S. Pat. No. 3,265,831, the relay could
be wired for normally open operation by connecting the conducting
lines to the terminal 187 and a terminal 193 that is electrically
integral with another stationary contact 195.
The operating structure 177 comprises an overcenter spring 197 that
is connected to the contact arm 179 to move the contact arm between
open and closed positions upon operation of the compensating
bimetal 175 and operating structure 177 in the manner more
specifically described in the patent to Ramsey et al. U.S. Pat. No.
3,265,831. A calibrating screw 201 (FIG. 7) is provided in each
pole unit to adjust the position of the associated bimetal 171 to
calibrate the pole unit.
When the current through any of the pole units of the relay 15
reaches a predetermined value such, for example, as 1.25 times the
full-load current of the motor that is to be protected by the
combination motor starter, the heat generated in the associated
heater structure 157 will cause the associated actuating bimetal
155 to flex to the left (FIG. 7) to thereby rotate the common
actuating bar 169 clockwise (FIG. 7) about the pivot 171. During
this movement, the projection 173 (FIG. 6) on the common actuating
bar 169 moves to move the compensating bimetal member 175 to
thereby move the operating structure 177 to operate the overcenter
spring 197 and contact arm 179 to move the movable contact 181 to
an open position disengaged from the stationary contact 183.
Following an operation of the relay 15, when the actuating bimetal
cools to the straightened position, the relay is reset in the
normally closed position seen in FIG. 6 either automatically or by
a hand-resetting operation as described in the above-mentioned U.S.
Pat. No. 3,265,831. As is described in U.S. Pat. No. 3,265,831, the
heaters are replaceable by heaters having different ratings and an
external adjustment is provided to enable a plus or minus
adjustment of the relay.
The operation of the combination motor starter will be best
understood with reference to FIGS. 1 and 2. As can be seen in FIG.
2, the combination motor starter 5 is shown diagrammatically to
illustrate an application of the motor starter for controlling and
protecting the motor circuit of a motor M. A pushbutton switch PB
may be mounted outside of the receptacle of the combination motor
starter 5 and wired to the motor starter 5 as shown. The pushbutton
switch may also be mounted on the motor starter enclosure if
desired. The overload relay is calibrated and provided with a rated
heater that will effect deenergization of the contactor to thereby
open the motor circuit, with a time delay, upon the occurrence of
overloads just over the motor full-load current, such as an
overload, for example, of 1.25 times the full-load current of the
motor. The circuit breaker is calibrated and adjusted to trip
faster than the relay at a first predetermined current which is
within a first predetermined range of from two to 13 times
full-load current of the motor, and preferably within the range of
from five to 13 times the full-load current of the motor. The
current-limiting fuse unit is constructed to operate faster than
the circuit breaker to interrupt the circuit at a second
predetermined current which is within a second range of from 50 to
200 times the full-load current of the motor and preferably within
the range of from 100 to 150 times the full-load current of the
motor. The current-limiting fuse unit will operate from the second
predetermined current to the maximum fault current that the
combination starter can interrupt with the current-limiting fuses
operating to limit the current thereby providing a high
interrupting capacity combination motor starter.
With the components connected and wired as shown in FIG. 2, an
operator can manually close the circuit breaker 9 and then operate
the pushbutton 209 to energize the motor M. Upon a closing
operation of the normally open pushbutton 209, a circuit is closed
from the line L1 through a line L4, the pushbutton 209, a line L5,
a line L6, the coil 129 of the contactor 113, the normally closed
contacts 181, 183 of the overload relay 15, a line L7, to the line
L2. This circuit energizes the coil 129 of the contactor 13 to pick
up the armature 131 (FIG. 5) of the contactor 13 to thereby close
the four pole units of the contactor 13. As can be seen in FIG. 2,
three pole units of the contactor 13 are in the three phases L1,
L2, L3 of the motor circuit and the fourth pole unit is provided to
hold in the contactor upon release of the pushbutton 209. With the
contacts 139, 137, 141 of the fourth pole unit of the contactor 13
closed, the contactor coil 129 will remain energized, to maintain
the contactor 13 closed, upon the release of the pushbutton 209
through a circuit that extends from the line L1, through the line
L4, normally closed pushbutton 213, a line L8, the contacts 139,
137, 141, the line L6, the coil 129 of the contactor 13, through
the normally closed contacts 181, 183 of the relay 15, the line L7,
to the line L2. The motor circuit will remain closed until the
pushbutton 213 is manually operated to deenergize the circuit of
the coil 129 or until one of the protective devices 9, 11, 15 is
automatically operated in response to an overload.
A specific example of a time-current application curve of the
combination starter is provided in FIG. 8. The combination starter
characteristics are illustrated in FIG. 8 as applied to control a
1-horsepower motor operating at 480 volts with a full-load current
of 1.8 amperes. As can be understood with regard to FIG. 8, the
motor will operate continuously at 1.8 amperes and at a very slight
overload of up to about 2.25 amperes. Upon the occurrence of an
overload of from about 2.25 amperes up to about 20 amperes, the
overload relay will operate, with a time delay according to the
heavy dotted overload relay curve from its top to point Z, to
deenergize the contactor to thereby interrupt the motor circuit.
Upon the occurrence of a fault current of from about 20 amperes to
about 240 amperes the circuit breaker will automatically trip
within a small fraction of a second to interrupt the motor circuit
according to the heavy solid circuit breaker trip curve from Z to
Y. Upon the occurrence of a fault current from about 240 amperes to
the interrupting capacity of the current-limiting fuse unit, it
will operate, with current-limiting action, to interrupt the motor
circuit in a time shown by the heavy dot-dash line from Y to its
lower end. The heavy dotted line curve plus the heavy solid line
curve and the heavy dot-dash line curve represents the overall
coordinated time-current curve characteristic of the complete
combination motor starter.
The current-limiting fuse unit has been successfully tested to
interrupt a 600-volt circuit in which 100,000 amperes symmetrical
is available and could flow when subjected to a short circuit if
the current-limiting function of the fuse were not present. The
fuses do not actually interrupt a current of 100,000 amperes but
have the property of limiting the rise of current and of
interrupting the circuit quickly, in a fraction of a half cycle,
before the instantaneous value of the current has risen to a peak
value more than a small fraction of the available short-circuit
current of the circuit. Thus, when the current-limiting fuse is
rated as having an interrupting capacity of 100,000 amperes it
means that the fuse will safely interrupt a circuit in which
100,000 amperes could flow when subjected to a short circuit, if
the current-limiting function of the fuse were not present. Upon
interruption by a fuse of the current-limiting fuse unit, enough
current is let through to automatically trip the circuit breaker,
thereby preventing the condition of having a three-phase motor
operate under single-phase power if a fault on a single conductor
of the three-phase circuit should blow only one fuse.
The locked rotor current of most motors is approximately six to 10
times the full-load current of the motor that is being protected.
Some motors may have locked rotor currents as low as three times or
as high as 13 times the full-load current. The commercially
available overload relays and contactors can safely operate to
interrupt the motor circuit upon the occurrence of the overloads of
from, for example, 1.25 times full-load current to six to 10 or 13
times full-load current. Any current that exceeds the locked rotor
current can be considered a fault current. Fault current, as the
name implies, is a direct result of some faulty condition in the
motor or its electrical circuit which reduces the resistance and
allows current to flow which is in excess of the intended design
values.
The circuit breaker 9 can be adjusted to trip upon the occurrence
of, for example, six to 10 times full-load current to thereby
interrupt the normal or low-level fault currents of the motor
circuit. For most applications, it is desirable to provide that the
trip adjustment of the circuit breaker cannot be set higher than
about 13 times the full-load current of the motor that is to be
protected by the combination motor starter. Thus, the circuit
breaker 9 comprises selective stop means (that can be selectively
positioned when the full-load current is determined) for providing
that the trip adjustment cannot be set higher than 13 times the
full-load current of the motor. When the stop means is selectively
positioned on the breaker, an operator will not be able to adjust
the breaker to start tripping at a current higher than 13 times the
full-load current of the motor.
The overload relay 15 has predictable heater burnout
characteristics. As can be seen in FIG. 8, the particular overload
relay in this application has a heater burnout or overload relay
damage curve, shown as a light dotted line, starting at
approximately 27 amperes. Prior to the crossover point (about 240
amperes) between the current-limiting fuse curve and the circuit
breaker curve, the circuit breaker will interrupt the current to
protect the heaters and overload relay. If the current-limiting
fuse unit were not utilized in the combination, the heaters would
be destroyed upon the occurrence of an overload above about 350
amperes since the breaker would not operate fast enough to protect
the heaters at this level of fault current. The damage in this case
could be substantially more severe than merely the heater burnout
since the relay and contactor could also be severely damaged at
this level of fault current if the circuit breaker were to be
relied on for interruption. It is noted, however, that with the
total coordinated curve the current-limiting fuse unit curve
crosses the circuit breaker curve at the point Y and in front of
the crossover point X of the overload relay and circuit breaker to
thereby provide protection of the overload relay heaters, overload
relay and contactor, along with more adequate protection of the
motor and cable of the motor circuit. Depending on the components
and characteristics of the combination motor starter and motor
circuit, the current-limiting fuse unit is designed to operate
within a range of from 50 to 200 times the motor full-load current
and preferably within the range of from 100 to 150 times the motor
full-load current to protect the components of the combination
motor starter, the cable, and the motor of the motor circuit.
As was hereinbefore set forth, the current-limiting fuse unit
operates, with current-limiting action, from the predetermined
current within the hereinbefore set forth range to the maximum
fault current that the combination motor starter can interrupt.
Upon interruption of the motor circuit by the current-limiting fuse
unit the circuit breaker 11 sees enough let-through current to
effect an automatic tripping operation.
It is seen from the foregoing description of the preferred
embodiment of the invention that there has been provided a
combination motor starter having the following advantages:
1. A closely coordinated protection system has been devised for
motor circuits with (a) a motor overload relay having a time delay
to prevent needless interruptions when there are harmless overloads
on the motor for only a short time, (b) a circuit breaker having an
instantaneous magnetic trip which is operable by low-fault currents
above the locked rotor current of the motor, and (c) a
current-limiting fuse which blows on a lower current than the
current at the intersection of the circuit breaker time-current
curve with the heater burnout or relay damage time-current curve,
so as to protect the motor overload relay from damage by larger
fault currents which could cause relay damage and other damage
before the circuit breaker opens the circuit.
2. The use of the magnetically tripped circuit breaker in the
combination gives maximum low-level fault protection and has the
advantages over the use of a fused disconnecting switch that (a)
the magnetically tripped circuit breaker can clear the fault faster
than a correctly applied fuse, because the fuse is inherently a
thermal device requiring time at low fault levels to acquire heat,
and must have a time delay built in to override the initial inrush
current peaks of motor starting, (b) there is a minimum of downtime
since the circuit breaker can be reclosed without the time required
to obtain replacement fuses, (c) single-phase operation of a
three-phase motor is prevented since the circuit breaker opens all
phases, (d) the cost of fuse replacements is greatly reduced since
the fuses used with the circuit breaker blow only on the infrequent
occasions when there is a high-level fault current, and (e) the
faster action of the circuit breaker in clearing low-level faults
minimizes the damage to the motor, its circuit and the components
of the combination motor starter. This is because most faults are
caused by insulation breakdown with a low level of fault current at
inception because of the high impedance of the fault, but if not
quickly arrested more insulation is burned away with a broadening
of the physical area of the fault and a lowering of the impedance
of the fault and a rapid rise in the fault current which will do
more extensive damage to all of the equipment in the circuit.
3. The use of the circuit breaker and current-limiting fuse in the
combination motor starter makes it possible to safely use the
combination device in circuits having an available short-circuit
current up to 100,000 amperes without losing the main advantages of
a circuit breaker device, and at the same time to protect the motor
relay against heater burnout or other damage.
* * * * *